Field of the Invention
This invention relates to a process for the partial oxidation of a sulfur- and silicate-containing carbonaceous fuel to produce a synthesis gas with reduced sulfur content. More particularly, this invention relates to a process for the partial oxidation of a sulfur- and silicate-containing carbonaceous fuel in the presence of a temperature moderator, an oxygen-containing gas, and a sulfur capture additive which comprises a calcium-containing compound portion, a sodium-containing compound portion, and a fluoride-containing compound portion to produce a synthesis gas with reduced sulfur content and a molten slag which comprises (1) a sulfur-containing sodium-calcium-fluoride silicate phase and (2) a sodium-calcium sulfide phase.
It is well known by those skilled in the art that synthesis gas comprising primarily H.sub.2 and CO, together with various amounts of other gases, may be produced via the partial oxidation gasification of a carbonaceous fuel at elevated temperatures. References disclosing such a process include co-assigned U.S. Pat. Nos. 2,818,326 (Eastman et al.), 2,896,927 (Nagle et al.), 3,998,609 (Crouch et al.), and 4,218,423 (Robin et al.), all incorporated herein by reference. Such carbonaceous fuels include crude residue from petroleum distillation and cracking processes, petroleum distillates, reduced crudes, whole crudes, asphalts, washed and unwashed coals, coal tars, coal derived oils, petroleum cokes, shale oils, tar sand oils, sludge and mixtures thereof. The production of synthesis gas from such fuels is described by, for example, co-assigned U.S. Pat. Nos. 3,544,291 (Schlinger et al.), 3,976,442 (Paull et al.) and 3,996,026 (Cole), all incorporated herein by reference.
It would be highly desirable to use comparatively low cost and readily available sulfur- and silicate-containing solid carbonaceous fuels for the production of synthesis gas comprising H.sub.2 and CO. However, in conventional partial oxidation gasification processes, sulfur-containing gases (e.g. H.sub.2 S and COS) in the amount of about 0.1 to 2.0 mole percent are produced along with the H2 and CO. These sulfur-containing gaseous impurities are undesirable, as they are pollutants, corrode piping and equipment upon contact, and deactivate downstream catalysts. Accordingly, raw gas streams from the reaction zone may require additional downstream gas purification in order to remove the sulfur-containing gases prior to the use of the synthesis gas in chemicals production, power generation, and the like.
Conventional processes employed in the downstream removal of sulfur and sulfur compounds from synthesis gas (often called acid gas removal processes) are described, for example, in R.F. Probstein and R.E. Hicks, Synthetic Fuels (1982) at pp. 210-21, and include both liquid absorption and solid absorption techniques. Such techniques generally require that the synthesis gas first be cooled from its production temperature of 1500-3000.degree. F., say 1700-2200.degree. F. to a lower temperature prior to removal of sulfur and sulfur-containing compounds. It would thus be advantageous to remove or reduce the concentration of sulfur and sulfur-containing compounds in the synthesis gas during or immediately after the production of the synthesis gas, while it is at high temperatures (i.e. in-situ sulfur removal). This would improve the thermal efficiency of the synthesis gas production process and in addition reduce costs associated with gas cooling and purification equipment and maintenance. References describing high temperature gas desulfurization are as follows:
Co-assigned U.S. Pat. No. 4,778,484 (Suggitt et al.), and incorporated herein by reference discloses a process for the production of desulfurized synthesis gas from a sulfur-containing carbonaceous fuel, the process comprising: (a) reacting a first portion of the fuel with an oxygen-containing gas and a temperature moderator to produce a synthesis gas; and (b) passing a second portion of the fuel in admixture with a portion of the synthesis gas and an iron-containing additive to a second reactor and thereby reacting to produce additional H.sub.2 and carbon oxides and particulate matter comprising iron oxysulfide derived from the interaction of the iron-containing additive and the sulfur-containing gases produced by partial oxidation of the fuel. In one embodiment of this invention, an alkali metal or alkali earth metal catalyst selected from Group IA or IIA of the Periodic Table of Elements is introduced into the second reactor in admixture with the fuel and iron-containing additive.
Co-assigned U.S. Pat. No. 4,776,860 (Najjar et al.) and incorporated herein by reference discloses a process for the production of desulfurized synthesis gas from a sulfur-containing carbonaceous fuel, the process comprising: (a) reacting a first portion of the fuel with an oxygen-containing gas and a temperature moderator to produce a synthesis gas; and (b) reacting a devolatized second portion of fuel and carbon from the unreacted first portion of fuel in a second reactor in the presence of a calcium-containing additive to produce additional H.sub.2 and carbon oxides and to achieve in-situ conversion of sulfur-containing gases (e.g. H.sub.2 S, COS) into calcium sulfide. In one embodiment of this invention, an alkali metal or alkali earth metal catalyst selected from Group IA or IIA of the periodic table is introduced into the second reactor in admixture with the fuel and iron-containing additive.
Co-assigned U.S. Pat No. 4,801,438 (Najjar et al.) discloses a process for the simultaneous partial oxidation and desulfurization of an ash-containing solid carbonaceous fuel to produce a synthesis gas low in sulfur. The process comprises reacting the fuel and a calcium-containing material in the presence of an oxygen-containing gas and a temperature moderator to produce synthesis gas and entrained molten slag in admixture with calcium sulfide and the silicates of calcium.
However, the aforesaid prior art does not teach or suggest the subject process which employs a novel sulfur capture additive which comprises a calcium compound portion, a sodium compound portion, and a fluoride compound portion that produces synthesis gas with a reduced sulfur content, and a novel molten slag with increased solubility for sulfur.